Investigations on CdTe-CdS solar cells on molybdenum foil substrates revealed that the depletion layer spans the entire US and CdTe film thickness and the cell should be conceived as a single junction device instead of the three separate junctions (Mo-CdTe, CdTe-CdS, CdS-TCO). Higher open circuit voltages were achieved when two US layers (separated by an air anneal) were used instead of a single US layer. The high series resistance of this solar cell continues to be the limiting factor in cell performance. Modeling and design issues for improving cell performance are presented. (C) 2002 Elsevier Science B.V. All rights reserved.